Aircraft wheel and brake systems generally include a non-rotatable wheel support, a wheel rotatably mounted to the wheel support, and a brake heat sink (or brake stack) having alternating brake disks (e.g., rotors and stators) mounted with respect to the wheel support and wheel for axial movement with respect to the wheel. In general, each rotor disk is coupled to the wheel for rotation with the wheel about a wheel rotation axis, and each stator disk is coupled to the wheel support in a non-rotatable manner. An end plate is located at one end of the brake stack, and a pressure plate is located at an opposite end of the brake stack. The rotors and stators are interleaved between the end plate and the pressure plate such that no two rotors and no two stators are adjacent to each other. An actuator ram is configured to apply pressure to the pressure plate, thereby compressing the brake stack to cause the brake disks to frictionally engage, to effectuate braking of the wheel.
The brake disks are generally annular in shape, with a thickness in the axial direction and a diameter in the radial direction, with respect to the axis about which the wheel rotates. An axle is configured to pass through an annular opening in the brake disks. The brake disks each have two friction surfaces: one facing axially toward the end plate and one facing axially toward the pressure plate. A line normal to each of the friction surfaces is substantially parallel to the axis about which the wheel rotates, such that a plane within which each brake disk lies is substantially orthogonal to the axis about which the wheel rotates.
In existing brake stacks, as the actuator applies pressure to the pressure plate and compresses the brake stack, the frictional forces between the brake disks may induce unwanted vibration in the brake system. For example, vibration levels in the brake housing, the axle, and the brake rod may reach undesirable levels during braking. Because the friction surfaces of the brake disks are substantially parallel to each other, vibration due to disk runout may occur, such as whirl vibration and rotor cycloidal vibration. In some existing hydraulic brake systems, orifices are used to facilitate damping of whirl vibration. In addition to increasing the weight of the brake system, the orifices add hydraulic response delay in antiskid modulation, increasing the required response time.
Additionally, in existing brake systems, as the actuator applies pressure to the break stack, the brake disks may move laterally and thereby cause uneven wear patterns on the brake disks. Attempts have been made to reduce this uneven wear by machining wear grooves into the brake disks during manufacture, but this extra production requirement increases cost because of the extra machining. The extra production also reduces the available wear area of the brake.
Generally, existing end plates are coned or tapered away from the brake stack and pucks may be used to reach back towards the brake stack to contact the brake disk neighboring the end plate. This configuration reduces the space available for the brake disks and adds weight due to the length of the pucks.
Accordingly, a brake stack with reduced vibration during a braking operation is desirable, and rotors and stators configured to remain substantially on center during braking are also desirable. Further, it is desirable to reduce weight and uneven brake wear and to increase anti-skid response time in braking systems.